In order to assure high quality castings, die cavities are evacuated prior to flow of molten material into the cavity. Prior systems include a vacuum device which is coupled through a vacuum supply system including conduits, filters and cut-off valves to the die cavity. In such systems, mechanical control means detect closure of a pour hole in the molten material transfer system to control the vacuum valves so as to communicate the die cavity with the vacuum device. The die cavity is evacuated. At fast shot the vacuum valve is closed to disconnect the vacuum system from the die cavity. Such cut-off valves, when closed, have the molten material pressures imposed thereon and high casting pressures can cause the vacuum valves to be plugged up.